1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device in which an oxide semiconductor is used.
2. Description of the Related Art
In recent years, a technique for forming a thin film transistor (also referred to as a TFT) using an oxide semiconductor and applying the thin film transistor to an electron device and the like has attracted attention. For example, a technique for forming a switching element of an image display device and the like using zinc oxide or an In—Ga—Zn—O based oxide semiconductor as an oxide semiconductor film is disclosed in Patent Document 1 and Patent Document 2.
Etching treatment is a typical technique for processing an oxide semiconductor (see Patent Document 3 and Patent Document 4); however, there are problem. For example, wet etching is unsuitable for miniaturization of an element since wet etching is isotropic etching. In addition, since a chemical solution is used in wet etching, there is a disadvantage in controllability. On the other hand, dry etching has advantages of miniaturization and controllability; however, there is a disadvantage in that an etching rate is small, so that it takes much time to perform treatment. In addition, there is a possibility that variation occurs in a surface to be etched depending on a device used.